1. ITT Course - Unit I --> Chapter 1 - Computer Concepts
Input Output Devices

2. ITT Course - Unit I --> Chapter 1 - Computer Concepts
Learning Objectives
To know about various input devices like keyboard, mouse, trackball, etc.
To discuss about various output devices like monitor, printer, etc.
To understand the classification of monitor, printer, etc.

3. An Introduction
Input / Output devices are those devices that allows computer to perform specific tasks as follows:-
Receive information for processing.
Return information after processing.
Store information.

4. Computer Organization (Generalized Approach)

5. Computer Organization (Specialized Approach)
Communication Devices
Secondary Storage
Input Devices
Output Devices
Control Unit
Arithmetic/
Logic Unit
Register Storage Area
Memory
Processing Device

6. Input-Process-Output Cycle

7. Input / Output Devices
Following categories of devices could be found in a computer:-
Input Devices : Input devices are those devices which are purely used for input purpose. For example, keyboard, mouse, etc. Input devices are used for entering data or instructions into a computer.
Output Devices: Output devices are those devices which are purely used for output purpose. For example, monitor, printer, etc.
Input and Output Devices: Input and Output devices are those devices which can act as input as well as output devices and can be used for both input and output purpose. For example, Hard Disk Drive, Magnetic Tape, Floppy Disk Drive.

8. Categories of Input Devices
Text Input Devices : Keyboard, etc.
Pointing Devices : Mouse, Light Pen, etc.
Gaming Devices : Joystick, Gamepad, etc.
Image, Video Devices : Image Scanner, Web Camera, etc.
Audio Input Devices : Microphones

9. Examples of Input Devices
Keyboard
Mouse
Trackball
Speakers
Scanner
Joystick
Web Camera
Touch Screen
Digitized Tablet
Digital Pen
MICR Device
OBR Device
OCR Device
OMR Device
Voice / Speech Recognition Device

10. Keyboard
A keyboard is an input device, partially modeled after the typewriter keyboard.

11. Keys on Keyboard Alphanumeric Keys
Alphabetical, numeric, and punctuation keys are used in the same fashion as a typewriter keyboard to enter their respective symbol into a word processing program, text editor, data spreadsheet, or other program.
Capital Alphabets A – Z
Small Alphabets a – z
Digits 0 – 9
Special Symbols #, $, %, ^, &, *, (, ), -, +, =, etc.

12. Keys on Keyboard Modifier Keys
Modifier keys are special keys that modify the normal action of another key, when the two are pressed in combination. For example, <Alt> + <F4> in Microsoft Windows will close the program in an active window.
The most widely-used modifier keys include the Control key, Shift key and the Alt key.
A Control key is a modifier key which, when pressed in conjunction with another key, will perform a special operation.
The Shift key is a modifier key which is used to type capital letters and other alternate "upper" characters.
The Alt key on a computer keyboard is used to change (alternate) the function of other pressed keys.
The Space bar, spacebar, or space key, is a key whose main purpose is to conveniently enter the space, e.g., between words during typing.
The Enter key causes a command line, window form or dialog box to operate its default function.

13. Keys on Keyboard Navigation & Typing Mode
Cursor movement keys / Arrow keys are buttons that are either programmed or designated to move the cursor in a specified direction.
The Page Up & Page Down keys are used to scroll up or down in documents.
The Home key is used to take the control to the start of the document.
The End key is used to take the control to the end of the document.
Tab key on a keyboard is used to advance the cursor to the next tab stop.
The Insert key is used to switch between the two text-entering modes.
The Delete key performs a function which discards the character ahead of the cursor's position, moving all following characters one position "back" towards the freed place.
Backspace is the keyboard key that moves the cursor one position backwards, deletes the preceding character, and shifts back the text after it by one position.
Scroll Lock is a key meant to lock all scrolling techniques.
Num Lock which is used to convert part of the main keyboard to act as a numeric keypad rather than letters.
The Caps Lock when pressed will set a keyboard mode in which typed letters are capitalized by default.

14. Keys on Keyboard System Command Keys
The Print Screen command used to capture the entire screen and send it to the printer, but in the present it usually puts a screenshot in the clipboard.
The Escape key (often abbreviated Esc) is used to initiate an escape sequence.
The Menu key / Application key is a key found on Windows-oriented computer keyboards. It is used launch a context menu with the keyboard rather than with the usual right mouse button.

15. Keyboard Types Keyboard Types Standard (QUERTY) Non-Standard
Standard keyboards are much just like the old typewriter
Non-Standard keyboards are specialized keyboard which serves a specific purpose.

16. Standard Keyboard
A basic computer keyboard that does not have any advanced features has 84 keys.
The multimedia computer keyboard has 101 keys and these keys are often referred to as shortcuts or hot keys.
Some multimedia keyboards have 104 keys and such devices provide more features as compared to a keyboard with 101 keys.

17. Standard Keyboard
84 Keys Computer Keyboard

18. Standard Keyboard
101 Keys Computer Keyboard

19. Standard Keyboard
104 Keys Computer Keyboard

20. Standard Keyboard
Laptop Size

21. Standard Keyboard
Gaming Keyboard

22. Standard Keyboard
Multimedia Keyboard

23. Standard Keyboard
Thumb Sized Keyboard

24. Standard Keyboard
Numeric Keyboard

25. Non-Standard Keyboard
Chorded Keyboard
Chorded Keyboard lets the user type in characters or commands by pressing a combination of keys.
The chorded keyboard design is typically used for hand-held computers that cannot accommodate standard-sized keyboards.

26. Non-Standard Keyboard
Touch Screen Keyboard
Touch screens come with a stylus, a pen-like device that doesn't have ink. This technology is typically used in products such as iPods and iPhones.

27. Non-Standard Keyboard
Virtual Keyboard
Virtual keyboards, such as the I-Tech Virtual Laser Keyboard, project an image of a full-size keyboard onto a surface. Sensors in the projection unit identify which key is being "pressed" and relay the signals to a computer or personal digital assistant. There is also a virtual keyboard, the On-Screen Keyboard, for use on Windows.

28. Non-Standard Keyboard
Foldable Keyboard
Foldable keyboards, as the name suggests, can be folded and made to fit into uneven spaces, so they can be very handy during travels.

29. Mouse
A mouse is a pointing device which is used to control & move the cursor on the screen.
“The first computer mouse underside view held by inventor Douglas Engelbart”

30. Mouse Buttons
This input device controls the cursor on the computer screen. It has two or three buttons and a cable connecting it to the computer. It is quite easy to operate a mouse, the user simply moves the cursor along the table. Once the cursor is at the desired location, the user can give instructions to the computer by clicking the button.

31. Types of Mouse Buttons Single Button Mouse Three Button Mouse
Five Button Mouse

32. Types of Mouse Serial Mouse
This type of mouse comes with a serial connector, it requires a free serial port on your PC.

33. Types of Mouse USB Mouse
This type of mouse has a USB connector and requires a free USB port to connect to the computer.

34. Types of Mouse Cordless Mouse
A cordless mouse (as the name suggests) has no cable, this type of mouse utilizes batteries for its power supply.

35. Types of Mouse Optical Mouse
An optical mouse utilizes optical electronics to track the mouse's position and movement, they are preferred over standard mechanical mice as they tend to be more reliable and require less maintenance.

36. Types of Mouse Laser Mouse
A laser mouse is a type of computer device that uses a laser beam rather than a ball to track the movement.

37. Common Mouse Operations
Click - pressing and releasing a button
(left) Single-click - clicking the main button.
(left) Double-click - clicking the button two times in quick succession counts as a different gesture than two separate single clicks.
(left) Triple-click - clicking the button three times in quick succession.
Right-click - clicking the secondary button
Drag - pressing and holding a button, then moving the mouse without releasing.
Button Chording
Combination of right-click then left-click.
Combination of left-click then right-click or keyboard letter.
Combination of left or right-click and the mouse wheel.
Clicking with a modifier key.

38. Trackball
A trackball is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation of the ball about two axes like an upside- down mouse with an exposed protruding ball.
The user rolls the ball with the thumb, fingers, or the palm of the hand to move a cursor.
Large tracker balls are common on CAD workstations for easy precision.
Trackballs have appeared in computer and video games.
The world's first trackball invented by Tom Cranston, Fred Longstaff and Kenyon Taylor working on the Royal Canadian Navy's DATAR project in 1952.

39. Scanner
A scanner is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image.
Scanners typically read red- green-blue color (RGB) data from the array. This data is then processed with some proprietary algorithm to correct for different exposure conditions, and sent to the computer via the device's input/output interface

40. The First Scanned Photo
History of Scanner
Scanners can be considered the successors of early telephotography input devices.
The First Scanned Photo

41. Types of Scanner Drum Scanner Flatbed Scanner Sheetfed Scanner
Film Scanner
Handheld Scanner
Cardscan Scanner

42. Drum Scanner
Drum scanners capture image information using photomultiplier tubes (PMT) technology unlike the charged coupled device (CCD) used in flatbed scanners and film scanners.
In the drum scanner the reflective & transmissive originals are mounted to an acrylic cylinder, the scanner drum, which rotates at high speed while it passes the object being scanned in front of precision optics that deliver image information to the PMTs.

43. Flatbed Scanner
A flatbed scanner is usually made of a glass pane, which is illuminated with a bright light found underneath, and a moving optical CCD or CIS array.
In the flatbed scanner images to be scanned are placed face down on the glass and the sensor and light source move across the glass pane reading the entire area.

44. Sheetfed Scanner
A scanner that allows only paper to be scanned rather than books or other thick objects.
It moves the paper across a stationary scan head.

45. Film Scanner
"Slide" (positive) or negative film can be scanned in equipment specially manufactured for this purpose.
Usually, uncut film strips of up to six frames, or four mounted slides, are inserted in a carrier, which is moved by a stepper motor across a lens and CCD sensor inside the scanner.

46. Handheld Scanner
A scanner that is moved across the image to be scanned by hand.
Handheld scanners are small and less expensive than their desktop counterparts, but rely on the dexterity of the user to move the unit across the paper.
Trays are available that keep the scanner moving in a straight line.

47. Cardscan Scanner
A business card scanner is a scanner that has only one purpose and that is to scan business cards and store the information.
A business card scanner scans business cards, separate out all their various types of information like name, title, address, phone number, address, URL, etc. and store that data, either with the help of a software that comes with the scanner, or in a personal information manager/address book packages such as Microsoft Outlook.

48. Joystick
A joystick is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling.
Joysticks are often used to control video games, and usually have one or more push-buttons whose state can also be read by the computer.
Joystick elements:
Stick
Base
Trigger
Extra buttons
Autofire switch
Throttle
Hat Switch (POV Hat)
Suction Cup

49. Web Camera
A webcam is a video capture device connected to a computer or computer network, often using a USB port or, if connected to a network, ethernet or Wi-Fi.
Their most popular use is for video telephony, permitting a computer to act as a video conferencing station.
A deaf or mute person using a Video Relay Service to communicate with a hearing person.

50. Microphones
Microphone is an input device which acts as an instrument and converts sound waves into an electric current, usually fed into an amplifier, a recorder, or a broadcast transmitter.

51. Touch Screen
A touch screen is a display that can detect the presence and location of a touch within the display area.
The term generally refers to touch or contact to the display of the device by a finger or hand.
Touch screens can also sense other passive objects, such as a stylus.
However, if the object sensed is active, as with a light pen, the term touch screen is generally not applicable.

52. Future of Touch Screen
“The future of touch screen seems bright. A company named synaptics is developing a touch screen called 'ClearPad'. It is a thin, high resolution capacitive touch screen that can be placed on top of any display where a finger-touch is required. If this technology is mass-accepted then the need of mechanical keys will be eliminated.”

53. Digitized Tablet
A graphics tablet (or digitizing tablet, graphics pad, drawing tablet) is a computer input device that allows one to hand-draw images and graphics, similar to the way one draws images with a pencil and paper.
A graphics tablet consists of a flat surface upon which the user may "draw" an image using an attached stylus, a pen-like drawing apparatus. The image generally does not appear on the tablet itself but, rather, is displayed on the computer monitor.
These tablets may also be used to capture data or handwritten signatures.
It offer a very natural way to create computer graphics, especially two-dimensional computer graphics.
Tablets are also popular for technical drawings and CAD.

54. MICR Device MICR stands for Magnetic Ink Character Recognition.
The machine recognition of numeric data printed with magnetically charged ink. It is used on bank checks and deposit slips.
It serves as a deterrent to fraud, because a photocopied check will not be printed with magnetic ink.
MICR readers detect the characters and convert them into digital data. Although optical methods (OCR) became as sophisticated as the early MICR technology, magnetic ink is still used.

55. OBR Device
A barcode reader (or barcode scanner) is an electronic device for reading printed barcodes. Like a flatbed scanner, it consists of a light source, a lens and a light sensor translating optical impulses into electrical ones.
Additionally, nearly all barcode readers contain decoder circuitry analyzing the barcode's image data provided by the sensor and sending the barcode's content to the scanner's output port.

56. Scanning Methods of OBR
Scanning methods are distinguished by the amount of operator manipulation required:
Pen or wand-type readers: requires the operator to swipe the pen over the code.
Semi-automatic handheld readers: The operator need not swipe, but must at least position the reader near the label
Fix-mount readers for automatic reading: The reading is performed laterally passing the label over the reader. No operator is required, but the position of the code target must coincide with the imaging capability of the reader.
Reader gates for automatic scanning: The position of the code must be just under the gate for short time, enabling the scanner sweep to capture the code target successfully.

57. Technologies of OBR Pen Type Readers
Pen type readers consist of a light source and a photodiode that are placed next to each other in the tip of a pen or wand. To read a bar code, the tip of the pen moves across the bars in a steady motion. The photodiode measures the intensity of the light reflected back from the light source and generates a waveform that is used to measure the widths of the bars and spaces in the bar code.
Dark bars in the bar code absorb light and white spaces reflect light so that the voltage waveform generated by the photo diode is a representation of the bar and space pattern in the bar code. This waveform is decoded by the scanner in a manner similar to the way Morse code dots and dashes are decoded.

58. Technologies of OBR Laser Scanners
Laser scanners work the same way as pen type readers except that they use a laser beam as the light source and typically employ either a reciprocating mirror or a rotating prism to scan the laser beam back and forth across the bar code. As with the pen type reader, a photodiode is used to measure the intensity of the light reflected back from the bar code. In both pen readers and laser scanners, the light emitted by the reader is tuned to a specific frequency and the photodiode is designed to detect only this modulated light of the same frequency.

59. Technologies of OBR CCD Readers
CCD readers (also referred to as LED scanner) use an array of hundreds of tiny light sensors lined up in a row in the head of the reader. Each sensor measures the intensity of the light immediately in front of it. Each individual light sensor in the CCD reader is extremely small and because there are hundreds of sensors lined up in a row, a voltage pattern identical to the pattern in a bar code is generated in the reader by sequentially measuring the voltages across each sensor in the row. The important difference between a CCD reader and a pen or laser scanner is that the CCD reader is measuring emitted ambient light from the bar code whereas pen or laser scanners are measuring reflected light of a specific frequency originating from the scanner itself.

60. Technologies of OBR Camera-Based Readers
2D imaging scanners are the fourth and newest type of bar code reader currently available. They use a small video camera to capture an image of a bar code. The reader then uses sophisticated digital image processing techniques to decode the bar code.

61. Technologies of OBR Omni-Directional Barcode Scanners
Omni-directional scanning uses "series of straight or curved scanning lines of varying directions in the form of a starburst, a pattern, or other multi-angle arrangement are projected at the symbol and one or more of them will be able to cross all of the symbol's bars and spaces, no matter what the orientation."
Omni-directional scanners almost all use a laser. Unlike the simpler single-line laser scanners, they produce a pattern of beams in varying orientations allowing them to read barcodes presented to it at different angles..
Omni-directional scanners are most familiar through the horizontal scanners in supermarkets, where packages are slid across a glass or sapphire window.
Omni-directional scanners are also better at reading poorly printed, wrinkled, or even torn barcodes.

62. OCR Device
OCR (Optical Character Recognition) is the mechanical or electronic translation of images of handwritten, typewritten or printed text (usually captured by a scanner) into machine-editable text. It is used to convert paper books and documents into electronic files, for instance, to computerize an old record-keeping system in an office, or to serve on a website.
When one scans a paper page into a computer, it produces just an image file, a photo of the page. The computer cannot understand the letters on the page, so you cannot search for words or edit it and have the words re-wrap as you type, or change the font, as in a word processor. You would use OCR software to convert it into a text or word processor file so that you could do those things. The result is much more flexible and compact than the original page photo.
OCR is a field of research in pattern recognition, artificial intelligence and computer vision.

63. OMR Device
OMR (Optical Mark Recognition) is the process of capturing human-marked data from document forms such as surveys and tests.
OMR Software is a computer software application that makes OMR possible on a desktop computer by using an Image scanner to process surveys, tests, attendance sheets, checklists, and other plain-paper forms printed on a laser printer.
There are many other applications for OMR, for example:
Process of institutional research
Community surveys
Consumer surveys
Tests / Assessments
Evaluations/ Feedback
Data compilation
Product evaluation
Time sheets / Inventory counts
Membership subscription forms
Lotteries / Voting
Geocoding (e.g. postal codes)

64. An OMR Sheet

65. Touch Pad Device
A touchpad (also trackpad) is a pointing device consisting of specialized surface that can translate the motion and position of a user's fingers to a relative position on screen.
They are a common feature of laptop computers and also used as a substitute for a computer mouse where desk space is scarce.
Touchpads vary in size but are rarely made larger than 40 square centimeters (about 6 square inches).
They can also be found on personal digital assistants (PDAs) and some portable media players.
Close up of a touchpad with a locking button on a Laptop

66. Back View of a Digital Camera
Digital Camera Device
A digital camera is a camera that takes video or still photographs, or both, digitally by recording images via an electronic image sensor.
Back View of a Digital Camera
Front View of a Digital Camera

67. Voice / Speech Recognition Device
Speech recognition (also known as automatic speech recognition or computer speech recognition) converts spoken words to text.
The term "voice recognition" is sometimes used to refer to speech recognition where the recognition system is trained to a particular speaker - as is the case for most desktop recognition software, hence there is an aspect of speaker recognition, which attempts to identify the person speaking, to better recognize what is being said.

68. Voice / Speech Recognition Device
Speech recognition applications include:-
Voice dialing
Call routing
Home automation appliance control & content-based spoken audio search
Simple data entry
Preparation of structured documents
Speech-to-text processing
Aircraft cockpits
Health Care
Military Services

69. Output Devices Monitors Printers Plotters Speakers Head Phones
Computer Output Microfilm (COM)

70. Computer Monitor
A monitor or display (sometimes called a visual display unit) is the screen on which words, numbers, and graphics can be seem.  The monitor is the most common output device.
CRT Monitor
The monitor comprises the display device, circuitry, and an enclosure.
The display device in modern monitors is typically a thin film transistor liquid crystal display (TFT-LCD), while older monitors use a cathode ray tube (CRT).
TFT Monitor

71. Imaging Technologies (Monitor)
As with television, many hardware technologies exist for displaying computer-generated output:
LCD (Liquid Crystal Display)
Passive LCDs are noted for poor contrast and slow response. They were used in laptops until the mid 1990s.
Thin film transistor. Nearly all modern LCD monitors are TFTs.
CRT (Cathode Ray Tube)
Raster scan computer monitors produce images using pixels. These were the most popular display device for older computers.
Vector displays, as used on the scientific & radar applications, & several early arcade machines such as Asteroids use CRT displays because of requirement for a deflection system, although a raster-based display may be used.
Television sets were used by most early personal and home computers. Resolution & image quality were limited by its display capabilities.
Penetron - military aircraft displays
Plasma display
Video projectors use CRT, LCD, DLP, LCoS, and other technology to emit light to a projection screen.
Surface-conduction electron-emitter display (SED) and field emission display (FED)
Organic light-emitting diode (OLED) display

72. Types of Monitor (Based on Color)
Monitors may be classified based on their color capabilities into three classes:-

73. Monochrome Monitor
Monochrome monitors actually display two colors, one for the background and other for the foreground.
The color can be black and white, green and black, or amber and black.

74. Grayscale Monitor
A gray-scale monitor is a special type of monochrome monitor capable of displaying different shades of gray color.

75. Color Monitor
Color monitor can display anywhere from 16 to over 1 million different colors.
Color monitors are sometimes called RGB monitors because they accept three separate signals – red, green and blue.

76. Types of Monitor (Based on Signals)
Monitors may be classified based on the signals into two classes:-

77. Analog Monitor
Analog monitors are traditional type of color display screen that has been for years in television.
Monitor that is capable of accepting continuously varying or analog signals from the video adapter. This allows the monitor to display an infinite range of different colors. The majority of all CRT monitors are analog monitors where all flat panel displays are digital.

78. Digital Monitor
Digital monitor accepts digital signals rather than analog signals.
Computer monitor that uses a digital signal instead of an analog signal. Unlike an analog monitor, a digital monitor has a set color range and is incapable of displaying an infinite range of colors.

79. Performance Measurement (Monitor)
The performance of a monitor is measured by the following parameters:
Luminance is measured in candelas per square meter.
Viewable image size is measured diagonally. For CRTs, the viewable size is typically one inch (25 mm) smaller than the tube itself.
Aspect ratios is the ratio of the horizontal length to the vertical length. 4:3 is the standard aspect ratio, for example, so that a screen with a width of 1024 pixels will have a height of 768 pixels. If a widescreen display has an aspect ratio of 16:9, a display that is pixels wide will have a height of 576 pixels.
Display resolution is the number of distinct pixels in each dimension that can be displayed. Maximum resolution is limited by dot pitch.
Dot pitch is the distance between pixels of the same color in millimeters. In general, the smaller the dot pitch, the sharper the picture will appear.
Refresh rate is the number of times in a second that a display is illuminated. Maximum refresh rate is limited by response time.
Response time is the time a pixel in a monitor takes to go from active (black) to inactive (white) and back to active (black) again, measured in milliseconds. Lower numbers mean faster transitions and therefore fewer visible image artifacts.
Contrast ratio is the ratio of the luminosity of the brightest color (white) to that of the darkest color (black) that the monitor is capable of producing.
Power consumption is measured in watts.
Viewing angle is the maximum angle at which images on the monitor can be viewed, without excessive degradation to the images, in degrees horizontally & vertically.

80. Printer
Printer is a device that prints text or illustrations on paper and in many cases on transparencies and other media.
It is a device that must be connected to a computer which allows a user to print items on paper, such as letters and pictures.
It can also work with digital cameras to print directly without the use of a computer.

81. Types of Printer

82. Impact Printers
Impact printers are those printer which produces text and images when tiny wire pins on print head strike the ink ribbon by physically contacting the paper. 
Impact printers are most functional in specialized environments where low-cost printing is essential. The three most common forms of impact printers are dot-matrix, daisy-wheel, and line printers.

83. Dot Matrix Printers
The technology behind dot-matrix printing is quite simple. The paper is pressed against a drum (a rubber- coated cylinder) and is intermittently pulled forward as printing progresses. The electromagnetically - driven printhead moves across the paper and strikes the printer ribbon situated between the paper and printhead pin. The impact of the printhead against the printer ribbon imprints ink dots on the paper which form human-readable characters.
Dot-matrix printers vary in print resolution and overall quality with either 9 or 24-pin printheads. The more pins per inch, the higher the print resolution. Most dot-matrix printers have a maximum resolution of around 240 dpi (dots per inch).

84. Daisy Wheel Printers
Daisy-wheel printers have printheads composed of metallic or plastic wheels cut into petals. Each petal has the form of a letter (in capital and lower- case), number, or punctuation mark on it. When the petal is struck against the printer ribbon, the resulting shape forces ink onto the paper.
Daisy-wheel printers are loud and slow. They cannot print graphics, and cannot change fonts unless the print wheel is physically replaced.
With the advent of laser printers, daisy-wheel printers are generally not used in modern computing environments.

85. Line Printers
Line printers have a mechanism that allows multiple characters to be simultaneously printed on the same line. The mechanism may use a large spinning print drum or a looped print chain. As the drum or chain is rotated over the paper's surface, electromechanical hammers behind the paper push the paper (along with a ribbon) onto the surface of the drum or chain, marking the paper with the shape of the character on the drum or chain.
Because of the nature of the print mechanism, line printers are much faster than dot-matrix or daisy-wheel printers. However, they tend to be quite loud, have limited multi-font capability, and often produce lower print quality than more recent printing technologies.

86. Non-Impact Printers
Non-impact printers are those which produces text and graphics on paper without actually striking the paper.
The main types of non-impact printers are thermal printer, laser printer, inkjet printer.

87. Thermal Printers
Characters are formed by heated elements being placed in contact with special heat sensitive paper forming darkened dots when the elements reach a critical temperature.
Thermal printer paper tends to darken over time due to exposure to sunlight and heat. The standard of print produced is poor.
Thermal printers are widely used in battery powered equipment such as portable calculators.
A Fax Machine uses a Thermal Printer

88. Inkjet Printers
Inkjet printers use quick-drying, water- based inks and a printhead with a series of small nozzles that spray ink onto the surface of the paper. The printhead assembly is driven by a belt- fed motor that moves the printhead across the paper.
Inkjets were originally manufactured to print in monochrome (black and white) only. However, the printhead has since been expanded and the nozzles increased to accommodate cyan, magenta, yellow, and black. This combination of colors (called CMYK) allows the printing of images with nearly the same quality as a photo development lab

89. Laser Printers
Laser printers are known for their high volume output and low cost-per-page. Laser printers are often deployed in enterprises as a workgroup or departmental print center, where performance, durability, and output requirements are a priority.
Laser printers share much of the same technologies as photocopiers. Rollers pull a sheet of paper from a paper tray and through a charge roller, which gives the paper an electrostatic charge. At the same time, a printing drum is given the opposite charge. The surface of the drum is then scanned by a laser, discharging the drum's surface and leaving only those points corresponding to the desired text and image with a charge. This charge is then used to force toner to adhere to the drum's surface.
The paper and drum are then brought into contact; their differing charges cause the toner to then adhere to the paper. Finally, the paper travels between fusing rollers, which heat the paper and melt the toner, fusing it onto the paper's surface.

90. Color Laser Printers
Color laser printers aim to combine the best features of laser and inkjet technology into a multi- purpose printer package.
The technology is based on traditional monochrome laser printing, but uses additional components to create color images & documents.
Instead of using black toner only, color laser printers use a CMYK toner combination. The print drum either rotates each color and lays the toner down one color at a time, or lays all four colors down onto a plate and then passes the paper through the drum, transferring the complete image onto the paper.
Color laser printers also employ fuser oil along with the heated fusing rolls, which further bonds the color toner to the paper and can give varying degrees of gloss to the finished image.
Because of their increased features, color laser printers are typically twice (or several times) as expensive as monochrome laser printers.

91. LED / LCD Printers
LED/LCD printers  are types of electro photographic printers that are identical to laser printers in most ways. Both LCD (liquid crystal display) and LED (light- emitting diode) printers use a light source instead of a laser to create an image on a drum.
In most contexts, "laser printer" covers LCD and LED printers as well. 
The print process is almost identical, but LED printers use Light Emitting Diodes to charge the drum, and the other uses Liquid Crystals.
These printers produce a very high quality text and graphics print out.

92. Solid Ink Printers
Solid Ink printers are page printers that use solid wax ink sticks in a "phase-change" process. They work by liquefying wax ink sticks into reservoirs, and then squirting the ink onto a transfer drum, from where it is cold- fused onto the paper in a single pass.  
Solid-ink printers offer better color consistency than do most technologies, with little variation caused by changes in temperature, humidity, or type of paper.
Solid ink machines have better reliability, because they have fewer components in comparison, for example with color laser printers .

93. Dye Sublimation Printers
Dye Sublimation printers are professional devices widely used in demanding graphic arts and photographic applications. True these printers work by heating the ink so that it turns from a solid into a gas. The heating element can be set to different temperatures, thus controlling the amount of ink laid down in one spot. In practice, this means that color is applied as a continuous tone, rather than in dots, as with an inkjet. One color is laid over the whole of one sheet at a time, starting with yellow and ending with black. The ink is on large rolls of film which contain sheets of each color, so for an A4 print it will have an A4-size sheet of yellow, followed by a sheet of cyan, and so on.
Dye sublimation requires particularly expensive special paper, as the dyes are designed to diffuse into the paper surface, mixing to create precise color shades.

94. Portable Printers
Portable printers are usually fairly lightweight and sometimes carry the option of using a battery instead of drawing power from the computer.
Usually they realize basic print resolutions suitable for plain text printing. In the market the following types of the portable printers are available:  Thermal printer, Thermal transfer printer and Ink-Jet printer.
The main advantage of thermal and thermal transfer printers is that they can be very small.
The smallest thermal and  thermal transfer printers  weigh  approximately one pound.
Usually the  ink-jet portable printer weighs more than 2 pounds. Thermal printers require a special type of paper.

95. Digital Photo Printers
Digital Photo printers Many middle range printers are now able to print photo quality images.
Usually an option with color printers, specialist photo print heads allow a greater resolution to be achieved to improve photo image quality.
Photo ink jet printers expand their gamuts by adding additional ink colors, usually light cyan and light magenta.

96. Network Printers
Network printer is a printer that provides output  capabilities to all network users.

97. EZ CD / DVD Printer
EZ CD/DVD Printers: provide a low cost way to create professional printed CD-Rs and
DVD-Rs. Instead of writing on the CD or applying labels, you can print directly on the CD surface! With high speed capabilities, a full color image can be printed directly on the top surface of your CDs in less than 1 minute.

98. Label Printer
Label Printers are  the smartest way to print labels one at a time.  The printers allow easy installation. 
High-quality, professional results is guaranteed every time.

99. VersaLaser Printer
VersaLaser™  (Universal Laser Systems Inc.) is peripheral tool, that  can transform images or drawings on your computer screen into real items made out of an amazing variety of materials… wood, plastic, fabric, paper, glass, leather, stone, ceramic, rubber… and it’s as easy to use as your printer.

100. 3D Printer
3D Printers (Z corporation). The ZPrinter 310 System creates physical models directly  from computer-aided design system  (“CAD”) and other digital data in hours instead of days. The printer is fast, versatile and simple, allowing engineers to produce a range of concept models and functional test parts quickly and inexpensively. The system is ideal for an office environment or educational institution, providing product developers easy access to a 3D Printer.

101. Characteristics of a Printers
Quality of Type: The output produced by printer is said to be ether letter quality, near letter quality, or draft quality.
Speed: Measured in characters per second or pages per minute, the speed of printer varies widely.
Impact or Non-Impact: Impact printers include all printers that work by striking an ink ribbon. Non-impact printers work as per electro-chemical technology.
Graphics: Some printers can print only text while other printers can print text as well as graphics.
Fonts: Some printers are limited to one or few fonts while some printers are capable of supporting unlimited variety of fonts.

102. Plotter
A plotter is a vector graphics printing device to print graphical plots, that connects to a computer.
Plotters are used primarily in technical drawing and CAD applications, where they have the advantage of working on very large paper sizes while maintaining high resolution.
Another use has been found by replacing the pen with a cutter, and in this form plotters can be found in many garment and sign shops.
There are two types of main plotters as:- Pen plotters & Electrostatic plotters.

103. Pen Plotter
Pen plotters print by moving a pen across the surface of a piece of paper.
Pen plotters can draw complex line art, including text, but do so very slowly because of the mechanical movement of the pens.
Pen Plotters are often incapable of creating a solid region of color.
Pen plotters have essentially become obsolete, and have been replaced by large-format inkjet printers and LED toner based printers.

104. Electrostatic Plotter
Electrostatic plotter is a plotter that uses an electrostatic method of printing. Liquid toner models use a positively charged toner that is attracted to paper which is negatively charged by passing by a line of electrodes (tiny wires or nibs). Models print in black and white or color, and some handle paper up to six feet wide. Newer electrostatic plotters are really large- format laser printers and focus light onto a charged drum using lasers or LEDs.
An Electrostatic Plotter produces a raster image by charging the paper with a high voltage. This voltage attracts toner which is then melted into the paper with heat.
This type of plotter is fast, but the quality is generally considered to be poor when compared to pen plotters.

105. Specialized Types of Plotter

106. Drum Plotter

107. Flatbed Plotter

108. Inkjet Plotter

109. Other Types (Cutting Plotter)

110. Other Types (Graph Plotter)

111. Speakers Speakers are used to play sound.
They may be built into the system unit or connected with cables.
Speakers allow a user to listen to music and hear sound effects coming from the computer system.
Some computer displays have basic speakers built-in.
Laptops come with integrated speakers.

112. Head Phones
Headphones are a pair of small loudspeakers, or less commonly a single speaker, with a way of holding them close to a user's ears and a means of connecting them to a signal source such as an audio amplifier, radio or CD player. They are also known as earphones, earbuds, stereophones, headsets.

113. A pair of supra-aural headphones
Types of Head Phones
Earbuds or earphones, such as these that ship with the Apple's iPod, rest in the outer part of the ear canal.
Circumaural headphones have large pads that surround the outer ear.
A pair of supra-aural headphones
Canalphones extend into the ear canal, facilitating greater dynamic range than earbuds as well as isolation from outside noise.

114. Input / Output Devices
A hardware device that accepts inputted information and also has the capability of outputting that information. Good examples of input/output devices are as follows:-
RAM
FDD
HDD
CD-RW
DVD-RW
Network Card
Modem
ZIP Drive
USB Drive
Magnetic Tape